James V. Bonta

Impacts of impervious surface on watershed hydrology: A review

Increased impervious surface area is a consequence of urbanization, with correspondent and significant effects on the hydrologic cycle. It is intuitive that an increased proportion of impervious surface brings with it shorter lag times between onset of precipitation and subsequently higher runoff peaks and total volume of runoff in receiving waters. Yet, documentation on quantitative relationships between the extent and type of impervious area and these hydrologic factors remains dispersed across several disciplines. We present a literature review on this subject to better understand and synthesize distinctions among different types of impermeable surface and their relative impacts, and describe the manner in which these surfaces are assessed for their putative impacts on landscape hydrology.

Factors affecting the identification of independent storm events

Abstract No standard method exists for identifying independent precipitation events for storm-based precipitation analyses. Two methods using Coshocton, Ohio data are compared in this study (the rank correlation and exponential methods), along with an investigation of factors affecting the minimum dry-period duration between storms (termed the “critical duration”). The exponential method gives higher critical duration estimates than the rank correlation method. The effect of sampling interval of the data on critical duration is small for both methods. Consequently, readily available hourly data may be used to estimate the critical duration. Year-to-year, seasonal and spatial variability in critical duration estimates are found to be great. About ten years of data are required to compute reliable estimates of critical duration. The exponential method is suggested for use.

Water quality response times to pasture management changes in small and large watersheds

To interpret the effects of best management practices on water quality at a regional or large watershed scale, likely response times at various scales must be known. Therefore, four small (≤1 ha [≤2.5 ac]) watersheds, in rotational grazing studies at the North Appalachian Experimental Watershed near Coshocton, Ohio, were used to study management impacts on water quality and response times. Surface runoff was sampled on an event basis; groundwater discharge was sampled monthly from springs developed where a perching clay layer outcropped at the soil surface. In four large watersheds ranging from 18 to 123 ha (44 to 303 ac), base flow was over 50% of annual stream flow and approximately 20% of annual precipitation. Nitrate-N loads in base flow were 31% to 59% of total annual NO3-N load in stream flow. When the N fertilization rate in a “medium fertility” area that contains two small watersheds was increased from 56 to 168 kg ha-1 y-1 (50 to 150 lb ac-1 yr-1), NO3-N concentrations in groundwater discharge responded little in four years. Then NO3-N levels in groundwater discharge increased for 10 years. With discontinuation of N fertilization, NO3-N concentrations in groundwater discharge returned to pre-N increase levels after six years. In a “high fertility” grazing area with a similar perched water table, 224 kg N ha-1 (200 lb ac-1) was applied annually. Concentrations of NO3-N increased to >10 mg L-1 (ppm) after five years. Legumes were then interseeded into the grass forage, and mineral N fertilization was discontinued. Nitrate-N concentrations in groundwater discharge returned to their pre-fertilization levels after about five years. This multi-year response of groundwater discharge quality to management change in small watersheds indicates that the response time for measurable change in multi-square-mile watersheds will be equally long, if not longer, and trends will be muted.

Impact of Using Paper Mill Sludge for Surface-Mine Reclamation on Runoff Water Quality and Plant Growth

Paper mills generate large amounts of solid waste consisting of fibrous cellulose, clay, and lime. Paper mill sludge (PMS) can improve reclamation of surface-coal mines where low pH and organic-carbon levels in the spoil cover material can inhibit revegetation. When applied at high rates, however, PMS may adversely impact the quality of surface runoff. Therefore, we applied PMS at 0, 224, and 672 dry Mg ha(-)(1) to 22.1 x 4.6-m plots at a recently mined site and monitored runoff for a total of 13 mo. The zero-rate plots served as controls and received standard reclamation consisting of mulching with hay and fertilization at planting. Compared to the control plots, PMS reduced runoff fourfold to sixfold and decreased erosion from 47 Mg ha(-1) to <1 Mg ha(-1). Most of the reduction occurred in the 2.5 mo before the plots were planted. Flow-weighted average dissolved oxygen concentrations in runoff from plots at the 224 and 672 Mg ha(-1) rates, however, were much lower (</=0.4 vs. 8.2 mg L(-1)) and chemical oxygen demand (COD) was much higher for the 672 Mg ha(-1) rate plots than the control plots during the pre-plant period (7229 vs. 880 mg L(-1)). There were few noteworthy differences in water quality among treatments post-planting, but plant dry-matter yields were greater for the PMS plots than for the controls. The 672 Mg ha(-1) rate did not increase COD or nutrient loads compared to the 224 Mg ha(-1) rate and may have more persistent beneficial effects by increasing soil organic carbon levels and pH to a greater extent.

Standardized research protocols enable transdisciplinary research of climate variation impacts in corn production systems

The important questions about agriculture, climate, and sustainability have become increasingly complex and require a coordinated, multifaceted approach for developing new knowledge and understanding. A multistate, transdisciplinary project was begun in 2011 to study the potential for both mitigation and adaptation of corn-based cropping systems to climate variations. The team is measuring the baseline as well as change of the systems carbon (C), nitrogen (N), and water footprints, crop productivity, and pest pressure in response to existing and novel production practices. Nine states and 11 institutions are participating in the project, necessitating a well thought out approach to coordinating field data collection procedures at 35 research sites. In addition, the collected data must be brought together in a way that can be stored and used by persons not originally involved in the data collection, necessitating robust procedures for linking metadata with the data and clearly delineated rules for use and publication of data from the overall project. In order to improve the ability to compare data across sites and begin to make inferences about soil and cropping system responses to climate across the region, detailed research protocols were developed to standardize the types of measurements taken and the specific details such as depth, time, method, numbers of samples, and minimum data set required from each site. This process required significant time, debate, and commitment of all the investigators involved with field data collection and was also informed by the data needed to run the simulation models and life cycle analyses. Although individual research teams are collecting additional measurements beyond those stated in the standardized protocols, the written protocols are used by the team for the base measurements to be compared across the region. A centralized database was constructed to meet the needs of current researchers on this project as well as for future use for data synthesis and modeling for agricultural, ecosystem, and climate sciences.

Sorbent-amended compost filter socks in grassed waterways reduce nutrient losses in surface runoff from corn fields

Surface runoff from row-crop fields frequently has high concentrations of sediment, nutrients, and pesticides, particularly in the first few events after tillage and agrochemical application. Compost filter socks placed in grassed waterways can further reduce sediment concentration as runoff is transmitted offsite but are generally ineffective in removing dissolved chemicals. Therefore, we investigated the effect of adding a proprietary sorbent, Nutriloxx, to filter socks filled with composted bark and wood chips on sediment, nutrient, and glyphosate concentrations in runoff. Surface runoff from one tilled and one no-till watershed planted to corn (Zea mays L.) was routed into two parallel, 30 m (99 ft) long, grassed waterways. Three, 46 cm (18 in) diameter filter socks filled with Nutriloxx-amended compost were placed 5 m (16.5 ft) apart across the upper half of one waterway and in the lower half of the paired waterway. Automated samplers were used to obtain samples above and below the treated waterway segments in the 2009 and 2010 crop years. The effectiveness of the grassed waterways and filter socks was highly dependent on tillage treatment and timing and size of the runoff events. In 2009, there were no sizable events during the early growing season. Consequently, erosion was minimal, and no significant effects on sediment concentration were detected. Averaged for both watersheds, however, the amended filter socks contributed to an additional 28% reduction in dissolved phosphate-phosphorus (PO4-P) concentration compared to waterway segments without filter socks (significant at p = 0.05). The filter socks, however, significantly increased sulfate (SO4) concentrations up to 20-fold in the first sampled event, but SO4 concentrations declined rapidly with subsequent events. Similarly, the filter socks increased concentrations of calcium (Ca), potassium (K), and sodium (Na), but this was not significant in all instances. In 2010, runoff-producing rainfall occurred frequently during the growing season, and the filter socks significantly decreased sediment and PO4-P concentrations from the tilled watershed. In addition, large reductions in ammonium-nitrogen (NH4-N) concentrations were noted (average > 7-fold), but field observations suggested that this was due to physical trapping of eroded coated-urea fertilizer prills rather than sorption. The filter socks continued to contribute to significantly increased SO4 concentrations from both watersheds. Filter socks can effectively reduce sediment losses when used in agricultural applications, and adding selective sorbents can increase their ability to retain nutrients. However, losses of sorbent components need to be considered.

Agricultural Policy Environmental eXtender model simulation of climate change impacts on runoff from a small no-till watershed

Long-term hydrologic data sets are required to quantify the impacts of management and climate on runoff at the field scale where management practices are applied. This study was conducted to evaluate the impacts of long-term management and climate on runoff from a small watershed managed with no-till (NT) system. The Agricultural Policy Environmental eXtender (APEX), a field scale hydrologic model which is capable of simulating the management and climate impacts on runoff, was used in this study. The specific objectives of the study were to (1) simulate the impacts of cropping management and tillage system on runoff and (2) simulate climate change impacts on runoff using different temperature, precipitation, and carbon dioxide (CO2) scenarios generated from the APEX model. The study was conducted on a small watershed located on the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio. This watershed (WS 118, ~0.79 ha [1.95 ac]) includes NT management with two periods of crop rotations: corn (Zea mays L.)–soybean (Glycine max L.)–rye (Secale cereale L.) (CSR; 2000 to 2005) and continuous corn (CC; 2006 to 2011). The results from this study indicate that the CSR rotation showed 37% lower simulated mean annual runoff compared with that of CC under NT system. The climate change scenarios indicated runoff was most sensitive to the precipitation, and interactions of precipitation, temperature, and CO2 concentrations. The highest increase of runoff (61%) was observed with 15% increase of precipitation, and the highest reduction in runoff (47%) with 15% decrease in precipitation, demonstrating the nonlinearity of hydrological systems. The results demonstrate the benefits of cover crops in the CSR over the CC rotation under NT system and show the significant impacts of climate change on runoff response from a small, upland, agricultural watershed. For future research, climate change impacts on runoff can be assessed using downscaled climate models that take into consideration interaction among weather parameters.

Watershed Research at the North Appalachian Experimental Watershed at Coshocton, Ohio

The North Appalachian Experimental Watershed (NAEW) at Coshocton, Ohio was established during the mid 1930s as one of the first watershed research locations in the US. The mission of the outdoor laboratory facility is to determine the effects of land-management practices on hydrology and erosion, to investigate scaling from small plots to large watersheds, and to determine rates and amounts of runoff from watersheds of varying configuration, shape, cover, topography, land-management practice. The NAEW infrastructure consists of approximately 1050 acres that includes large lysimeters, small and large experimental watersheds, and a network of rain gauges. One of the first land-management practices investigated was an intensive study on the effects of a crop rotation on steep watersheds with different soils. These early studies contributed to the development of the no-till concept for farming steep lands to reduce erosion and runoff. No-till has been investigated continuously for 43 years at the NAEW with the current emphasis on effects on soil quality, carbon sequestration, and crop residue removal for biofuel production. Data from Coshocton were included in the original development of the curve number method, which is used worldwide. Watershed studies investigations include effects of conservation tillage, herbicide and nutrient management, pasture management, coal mining and reclamation, and urbanization on hydrology and water quality. Other studies conducted throughout the history of the NAEW include those on rain gauges, soil carbon, evapotranspiration, precipitation simulation, ground-water recharge, curve numbers, macropores, hydraulics, watershed modeling, and instrumentation development. Expertise and data at the NAEW are sought after worldwide on these topics. The facility has unique features that enable it to contribute to watershed model component development, including identification and quantification of the processes of preferential flow, interflow, non-uniform runoff generation, and scaling. The NAEW continues to have an important impact on soil and water conservation.

Drop-box weir for measuring flow rates under extreme flow conditions

Measuring discharge rates in stream flows laden with sediment using precalibrated flow structures, such as flumes and weirs, is difficult and flow measurements can quickly become inaccurate. This is because large particles ranging from sand-sized particles to rocks easily clog the structures, changing the approach velocities and flow directions during a runoff event. These conditions often occur during extreme runoff events when there is sufficient transport capacity in the flows, causing deposition. Furthermore, assumptions are often made for individual structures regarding the approach conditions in a stream channel, such as a minimum channel slope and direction of flow. The drop-box weir is one of two flow-measuring devices (the other is the critical-depth flume) that can be used to monitor under these conditions and give accurate flow measurements. The operating principle of the drop-box weir is to maximize the turbulence in stream flows to suspend large sediment particles. This is accomplished by forcing two water streams to flow into each other from opposite sides of a box, after falling into the box. The box is located upstream from a V-measuring section. At low flow rates, the water streams enter the box toward the front near the V section. At increasingly larger

Simulating Runoff from Small Grazed Pasture Watersheds Located at North Appalachian Experimental Watershed in Ohio

ABSTRACT Runoff from grazing pasture lands can impact water quality in receiving streams if not well managed. Management consists of conservation practices to reduce runoff and pollutants transport. Simulation models have been effectively used to design and implement these conservation practices. The Agricultural Policy Environmental Extender (APEX), a process-based hydrologic model, was used in this study to simulate the management impacts on surface runoff from three small grazed pasture watersheds located at the North Appalachian Experimental Watersheds near Coshocton, Ohio. Specific objectives of this study were to 1) calibrate the APEX model and test runoff predictions against measured runoff and 2) simulate the long-term impacts of different management scenarios on surface runoff. Results show that the APEX model simulated surface runoff reasonably well with the coefficient of determination (R2) and Nash-Sutcliffe efficiency values varying from 0.49 to 0.72 and from 0.25 to 0.60 for calibration and validation, respectively. After validation, the APEX model was run for 37 yr (1975–2011) for long-term scenarios to analyze the impacts of soil properties and management on surface runoff. Data from this study indicated that keeping the watershed land use as a hay meadow instead of grazing significantly reduced cumulative runoff by 58–67%. Buffer strips of perennial grasses resulted in decreased simulated runoff. To simulate the impacts of soils on runoff, the surface (0–5 cm) soil properties of the toe position were applied to the entire grazed watershed. Subsequently, the increase in soil richness resulted in reduction (≤5%) in surface runoff. The simulation results from the present study demonstrate the benefits of hayed meadow over grazed pasture and further predict the decreased trend of runoff due to soil properties change and buffer strips.